Method for manufacturing heavy duty bags

ABSTRACT

A method for manufacturing heavy duty bags wherein stretched tapes made of synthetic resin such as high density polyethylene or polypropylene are spirally wound in opposite directions in a manner to intersect each other to form a plurality of superposed cylindrical bodies. The superposed portions of the intersecting stretched tapes forming said cylindrical bodies are bonded together to form a cylindrical network, one end of which is sealed to provide a bottom.

United States Patent Sato et al.

METHOD FOR MANUFACTURING HEAVY DUTY BAGS Inventors: Wasuke Sato,Kawasaki; Fumio Iriko, Tokyo; Sadao Yamamoto, Kawasaki; MitsumaroFujisawa; Shigeyuki Hatakeyama, both of Yokohama, all of Japan Assignee:

Filed:

Showa Denko K.K., Tokyo, Japan Nov. 10, 1970 Appl. No.: 88,381

Related US. Application Data Division of Ser. No. 847,647, Aug. 5, 1969,Pat. No. 3,570,749.

Foreign Application Priority Data Aug. 9, 1968 Japan 43-56113 Dec. 20,1968 Japan ..43-1l0790 Dec. 20, 1968 Japan ..43; 10Z9.1 Apr. 11, 1969Japan 44-32513 Apr. 11, 1969 Japan 44-32514 Apr. 11, 1969 Japan 44-32515US. Cl. 93/80, 156/430 Int. Cl. B316 1/00 Field of Search93/80 R, 35 MW;156/427, 195, 156/429, 430

[ Jan. 29, 1974 [56] References Cited UNITED STATES PATENTS 3,257,9156/1966 Cartier et a]. 93/35 MW 2,213,290 9/1940 Rowe 93/80 UX 2,777,501l/l957 Fischer 93/80 X 3,515,621 6/1970 Watson 156/430 X 3,004,58510/1961 Lewis et a1 156/429 FOREIGN PATENTS OR APPLICATIONS 474,7714/1929 Germany 93/80 Primary ExaminerAndrew R. Juhasz AssistantExaminerLeon Gilden Attorney, Agent, or Firm-Flynn & Frishauf [5 7]ABSTRACT A method for manufacturing heavy duty bags wherein stretchedtapes made of synthetic resin such as high density polyethylene orpolypropylene are spirally wound in opposite directions in a manner tointersect each other to form a plurality of superposed cylindricalbodies. The superposed portions of the intersecting stretched tapesforming said cylindrical bodies are bonded together to form acylindrical network, one end of which is sealed to provide a bottom.

3 Claims, 33 Drawing Figures PAIENIE JAMES 1m SHEET 01 0F FIG.

FIG. 3

Pmmmm 3,788.199

SHEET 02 0F 10 SHEET 03 0F PATENTEB JAN 2 9 1974 FIG. 6

PATENTEB JAN 2 9 I974 SHEU 06 0F PATENTH] JANE 915?! SHEEI 07 0FPATENTEU JAN 2 915M SHEET 08 0F FIG. 21

FIG. 22

I PATENTEUJAHZQ 1974 SHEET DSUF 10' METHOD FOR MANUFACTURING HEAVY DUTYBAGS This is a division of Application Ser. No. 847,647, filed Aug. 5,1969 now U.S. Pat. No. 3,570,749.

The present invention relates to a method for manufacturing heavy dutybags used in storing or transporting cereals, fertilizers or othergranular or powdered product of relatively great weight.

Since stretched tapes made of high density polyethylene or polypropylenedisplay extremely high tensile strength, they are employed in variousapplications such as fabric prepared by weaving said tapes as a warp andwoof (normally, plain fabric) or composite articles formed by laminatingsynthetic film with said fabric. Particularly in recent years, fabricwoven from the aforesaid stretched tapes is widely used as the materialof such heavy duty bags instead of the heretofore used hemp. Use of thestretched tapes has permitted the manufacture of bags which can fullywithstand heavy loads resulting from piling up or falling impacts.

However, the operation of weaving fabric from the aforementionedstretched tapes has heretofore presented difficulties in increasingefficiency. This in turn has obstructed reduction in the manufacturingcost of stretched tape cloth and in consequence formed a bottleneck to'.the production ofinexpensive heavy duty bags.

The object of the present invention is to eliminate the drawbacksencountered with the prior art and provide a novel type of heavy dutybags which can be prepared from synthetic resin stretched tapes withhigh efficiency without weaving.

SUMMARY OF THE INVENTION According to the present invention, a heavyduty bag is prepared by spirally winding'stretched tapes of syn theticresin in opposite directions in a manner to intersect each other to forma plurality of superposed cylindrical bodies, bonding together thesuperposed portions of the intersecting tapes constituting thecylindrical body (the term bonding as used in this specification denotesnot only bonding by means of an adhesive agent but also by thermalfusion) to form a cylindrical network, or bonding synthetic resin filmto one or both sides'of said network to form a cylindrical compositebody and sealing one end of thecylindrical network or composite body toprovide a bottom.

Among the stretched tapes made of synthetic resin, the one of highdensity polyethylene or polypropylene is particularly preferable-due toits extremely high tensile strength. The film used in preparing theaforesaid network-film composite body consists of polyethylene,polypropylene, polyvinyl chlorideor other types of synthetic resin.These raw materialsmay be selectively used according to the applicationin which the subject heavy duty bag is employed.

The spirally wound inner and outer stretched tapes of the superposedcylindrical bodies may intersect each other at suitable angles dependingon the application intended. However, it is preferred that a heavy dutybag manufactured accordingto the present invention have substantiallyequal longitudinal and transverse strength. To this end, it is advisableto allow the tapes to intersect each other at an angle of about 90".Also, the width and number of the stretched tapes and the space at whichthey are wound may be selectively defined according to the applicationin which the bag is used. Referring to, for example, the intertapespace, where the bag is desired to hold fine powders or be airtight, thetapes are spirally wound in such a manner as to allow their edges to beclosely attached to or slightly overlap each other. Again where the bagis demanded to have breatheability, the tapes are wound so as to allowfor a suitable space therebetween.

The present invention enables a heavy duty bag to be manufactured inhigh efficiency by the later described simple process. Accordingly, theinvention drastically cuts the cost of a bag as compared with the oneobtained by the prior art involving weaving (and lamination). Moreover,the bag according to the invention has a remarkably great mechanicalstrength. Further, the present heavy duty bag is prepared simply bysealing one end of a cylindrical network or network-film composite bodyto form a bottom, so that there is no need to seal the bag edges as isthe case with the prior art which prepared a bag from flat sheeting. Inthis respect,

too, the present invention has the advantage of simplifying the processof manufacturing bags.

The present invention can be more fully understood from the followingdetailed description when taken with reference to the accompanyingdrawings, in which:

FIG. 1 is a plan view of a bag-manufacturing apparatus used in thepresent invention;

FIG. 2 is a cross-section on line Illl of FIG. 1;

FIG. 3 is a schematic illustration of the manufacturing process of aheavy duty bag by the apparatus of FIG. 1;

FIG. 4 is a perspective view of a heavy duty bag prepared by theapparatus of FIG. 1;

FIG. 5 is an elevation of another apparatus used in the invention;

FIG. 6 is a cross section on line VIVl of FIG. 5; FIG. 7 is a crosssection on line VII-VII of FIG. 6;

FIG. 8 is an enlarged cross section of the C portion of FIG. 5;

FIG. 9 is an elevation of part of still another apparatus used in theinvention;

' FIG. 10 is a cross section of that part of a further apparatus used inthe invention which corresponds to FIGS. 18 to 20 are enlarged crosssections of the bag materials used in another type of heavy duty bagaccording to the invention;

FIGS. 21 and 22 are elevations, with part broken away, of still anothertype of heavy duty bag according to the invention;

FIG. 23 is an elevation, with part broken away, of still another type ofheavy duty bag according to the invention;

FIG. 24 is a cross section on line XXIVXXIV 0 FIG. 23;

FIG. 25 is an elevation, with part broken away, of a further type ofheavy duty bag of the invention;

FIG. 26 is a cross section on line XXVI-XXVI of FIG. 25;

FIG. 27 is a perspective viewof a modification of the material of aheavy duty bag prepared from a cylindrical network-film composite body;

FIG. 28 is a perspective view, with part broken away, of the bagmaterial of FIG. 27, whose lower half is turned over so as to besuperposed on the upper half;

FIG. 29 is a perspective view of a heavy duty bag prepared by sealingone end of the bag material of FIG. 28;

FIGS. 30A and 30B jointly present a perspective view of anothermodification of the material of a heavy duty bag prepared from acylindrical network-film composite body;

FIG. 31 is a perstpective view, with part broken away, of the conditionin which the inner and outer bag materials of FIGS. 30A and 30B aresuperposed; and

FIG. 32 is a perspective view ofa heavy duty bag prepared by sealing oneend of the superposed assembly of the bag materials of FIG. 31.

There will now be described with reference to the appended drawings aheavy duty bag according to the present invention and a-method formanufacturing the same.

Referring to FIGS. 1 and 2, there is rotated a suitable cylindricalmember 2 covered with cylindrical synthetic resin film.l around the axisAA using a drive mechanism 3. The cylindrical member 2 is supported byits support means 4 disposed on both sides thereof in such a manner asto be detachable from either of them. The stretched tape 6 taken up on abobbin is wound on the surface of the film I while an adhesive 8 isbeing applied on said tape 6 using a coating roll 7. The bonding of thetape 6 to the film is effected by a press roll 9. The supporting means10 of the bobbin 5 is transferred by a chain device 11 moved by a drivemechanism 12 along the axis AA of the cylindrical member 2 andinterlockingly with its rotation, thereby causing the stretched tape tobe spirally wound about the cylindrical member 2.'When the spiralwinding of the stretched tape 6 about the cylindrical member 2 startingwith one end 13 of the cylindrical film l is finished at the other end14 of said film 1, then there is actuated a limit switch 15 disposedunder the suppport means 10 of the bobbin 5 to cause the drive mechanism12 to rotate in the opposite direction. This reverse rotation istransmitted to the chain device 11 toallow the support means 10 of thebobbin 5 to be transferred in the opposite direction to the previouscase, so that the stretched tape 6 is wound about the film 1 startingthis time with the end 14 towardthe end 13 in the reverse spiral form asillustrated in FIG. 3. If the aforementioned winding operation isrepeated as often as required, then there is produced a network-filmcomposite body 16 as shown in FIG. 4 because a network consisting ofintersecting stretched tapes is bonded to the surface of the cylindricalsynthetic film. When said composite body 16 is sealed at one end afterbeing taken off the cylindrical member 2, there is obtained a heavy dutybag formed of said composite body 16.

In addition to the aforementioned method, bonding may be made by anotherprocess which consists in previously coating that plane of the stretchedtape 6 which requires bonding with commercially available dry laminationadhesive or hot melt adhesive and, after being dried, taking up saidtape 6 on the bobbin 5, thereafter winding said coated tape 6 around thesurface of the film 1 and bonding a network consisting of said stretchedtape to the film 1 by heating the press roll 9 to 60 to 90C. If thereare provided a plurality of bobbins 5 for the stretched tape 6, theaforementioned bonding methods enable a plurality of stretched tapes 6to be fed to the bag manufacturing machine at the same time. Further,bonding may be made by a process which involves the use of two bobbinscombined with a drive mechanism and winds and bonds two tapes on to acylindrical synthetic resin film 1, starting with both ends of said film1 toward the respective opposite ends. It will be apparent that theaforesaid various bonding methods may be employed in suitablecombination and also the process of previously coating the stretchedtape with an adhesive may be incorporated in any or combination of theaforesaid bonding methods. Each of the foregoing bonding methods isuseful in elevating the efficiency of manufacturing a heavy duty bag.

There has been described a heavy duty bag and a method for manufacturinga heavy duty bag from a composite body consisting of a cylindricalnetwork and film. Also where the bag is only formed of a cylindricalnetwork, there can be used substantially the same process as in thepreceding case with some slight modifications, excepting that acylindrical form of synthetic resin film is omitted, Namely, when thestretched tape is initially wound its loading end should be fixed on thecylindrical member 2 by suitable means, and the adhesive agent shouldpreferably be applied only to those parts of' intersecting stretchedtapes which are superposed on each other. To this end, it will beadvisable to adopt such arrangement as'to allow, for example, thecoating roll 7 of FIGS. l and 2 to intermittently contact the tape 6 andoperate said roll 7 each time those respective lengths of theintersecting tapes 6 which are defined between the superposed parts arefed to the coating device.

The diameter of the cylindrical member 2 is determined according to thedesired measurements of a heavy duty'bag manufactured from a network ora network-film combination. For a practical bag manufacturing apparatus,therefore, it is convenient to provide a plurality ofcylindrical members2 and use them intere seeb y- The angle at which the'stretched tape 6 iswound .about the cylindrical member 2 or the cylindrical form ofsynthetic resin film covering said member 2 may be chosen as described.I-Iowever,.if the tape 6 is wound at an angle of approximately 45 withrespect to the axis AA of the cylindrical member 2, then there will beobtained a bag having-substantially the same longitudinal and transversemechanical strength in which the tapes intersect each other at an angle'of about There will now be described by reference to FIGS. 5 to 15another method for manufacturing a heavy duty bag according to thepresent invention. Throughout FIGS. 5 to 8, numeral 17 denotes anendless belt. As illustrated, there are provided four endless belts.These endless belts are arranged on an inner frame 18 in such a mannerthat their outer strips are equally spaced from I each other in aperipheral, direction and that if said outer strips are further extendedin a peripheral direction they will assume a substantially cylindricalform having an octagonal cross section as shown in FIG. 6. The outerstrips of the belts 17 are made to travel upward (as indicated by thearrow) at the same speed along the axis BB of the cylindrical form asreferred to above. Numerals 20 and 19 represent upper and lower holdingmeans, which rotatably support one or more (eight as shown) bobbins 21and 22 (these numerals denote upper and lower groups of bobbins) abouteach of which there are respectively wound upper and lower groups 23 and24 of adhesive stretched tapes made of synthetic resin. The upper andlower holding means 20 and 19 are allowed to rotate in oppositedriections at the same speed on upper and lower annular rails 28 and 27fixed on upper and lower outer frames 26 and respectively by a drivemechanism consisting of a prime mover 29, upper and lower pulleys 31 and30, upper and lower belts 33 and 32 and gear 34.

The lower group 23 of adhesive stretched tapes made of synthetic resinis wound about the aforesaid octagonal form defined by the outer stripsof the endless belts 17. While the endless belts 17 are being operated,the lower tape holding means 19 is allowed to rotate around theoctagonal cylindrical form. Then said tapes 23 are spirally wound toform an octagonal cylindrical body. On the other hand, the upper tapeholding means 20 is made to rotate in the opposite direction to thelower holding means 19. Then the upper group 24 of stretched tapes isspirally wound in the opposite direction to the lower tapes 23 on theoutside thereof in a manner to intersect them, similarly forming anoctagonal cylindrical body. Bonding of the superposed portions of theintersecting tapes 23 and 24 allows an octagonal cylindrical network 35to be continuously drawn out at the upper ends of the endless belts 17.Said network is pressed between the press rolls 36 to ensure bonding,drawn out in a flattened cylindrical body 37 and cut to a suitablelength. When the cut portion of the network is sealed at one end thereis obtained a desired heavy duty bag. Further, if required, there areprovided one or more groups of supplementary rolls 38 to prevent themeshes of the octagonal cylindrical network 35 from being deformed whenit is flattened.

FlG.7 is a cross section on line VIIVll of FIG. 6k presenting in detailthat part of a bag manufacturing apparatus used in the present inventionshown in FIG. 5 which is associated with the endless belts 17. One theoutside of the inner frame 18 set up on a bed are fitted a plurality ofbrackets 39 There are provided a plurality of rolls 40, 41 and 42 whoseaxles are supported by the brackets 39, and there is stretched eachendless belt l7over said rolls 40, 41 and 42. The uppermost andlowermost rolls and 41 are driven by a prime mover and transmissionmechanism 46 interlockingly with a chain 43 and chain wheel 44 so as tollow the outer strip of ach endless belt 17 to travel upward. Theremaining roll 42 is used as a free guide roll and there are provided arequired member thereof to prevent the warp of the endless belt 17. Therespective endless belts 17 are so adjusted as to travel at an equalspeed. The endless belt 17 may consist of any material if it ismechanically strong and not subject to warping, for example, a thinstainless steel plate, fabric, cordincorporated rubbers used singly orin combination.

Where the tape is thermally bonded, it should withstand said bondingtemperature.

FIG. 8 is an enlarged section of the C portion of FIG. 5 for betterunderstanding of the tape holding means and bobbin assembly. The sameparts of FIG. 8 as those of FIGS. 5 to 7 are denoted by the samenumerals.

The foregoing relates to the case where there are combined four endlessbelts to assume a cylindrical form having an octagonal cross section.The cross section is preferred to approximate a circular form as much aspossible, so that it is desired to combine a larger number of endlesbelts. Since, however, such arrangement leads to the complicatedconstruction of a bag manufacturing apparatus, it is only recommendedwhere it is intended to manufacture a heavy duty bag of relatively largediameter.

Tape bonding may be made by directly heat sealing tapes using the pressrolls 36 as heat rolls or by another process which consists in coatingthe outer surface of the tape 23 constituting the inner portion of acylindrical network and/or the inner surface of the tape 24 forming theouter protion of the cylindrical network with a thermosettingsolution-type adhesive having a long pot life, followed by drying, orpreviously taking up on a bobbin a tape coated with a hotmelt adhesiveand then cooled, pressing the tape between the press rolls 36 used asheat rolls and, if required, later subjecting it to further coolingusing separate cooling rolls. It will be apparent that with respect totape bonding, there may also be adopted a mechanism which continuouslyapplies an adhesive on the superposed portions of intersecting tapesjust before they are introduced into the manufacturing apparatus.

The angle defined by the tapes 23 and 24 constituting the cylindricalnetwork 37 with the axis BB of said network and the angle at which saidtapes 23 and 24 intersect each other may be freely determined by varyingthe interrelationship between the travelling speed of the endless belts17 and the rotating speed of the tape holding means 19 and 20. However,if the tapes 23 and 24 are so wound as to define an angle of about 45with the aforesaid axis BB, it will be most preferable, because there isobtained a bag having a great mechanical strength in which said tapes 23and 24 intersect each other at an angle of about The number of bobbinsfitted to the tape holding means 19 and 20 is suitably determinedaccording to the angle defined by the tapes with the axis BB, theirwidth and interspace.

FIG. 9 represents the case where there are used long endless belts andfour tape holding means. Namely, the interspace between the tapes 49 and50 supplied from the lower two tape holding means 47 and 48 is filledwith the tapes 53 and 54 introduced from the upper two holding means 51and 52. Such a device produces a stronger heavy duty bag in which thecylindrical network is formed of apparently entwined tapes.

For uniform and firm bonding of tapes, it is preferred that of theperiphery of a cylindrical form defined by endless belts having apolygonal cross section, that part occupied by the belt be as broad aspossible. Such arrangement can be realised by using solft belt materialand special-shaped guide rolls 55 and 56 having a cross section as shownin FIG. 10. Also in this case, however, the bag manufacturing apparatuswill unavoidably become relatively complicated in design. For easyresolution of this problem, there is recommended a device jointlyindicated by FIGS. 11 and 12. As apparent from FIG. 11, there are usedupper and lower groups 17a and 17 of endless belts to provide acylindrical form. Namely, the endless belts are arranged in such amanner that as in the direction of the axis DD of said cylindrical form,the outer surfaces on both sides of the respective endless belts make upfor each other. Further, the upper and lower endless belts are providedwith supplementary rolls 38a and 38 respectively. Such a device ensuresthe firm bonding of all the superposed parts of intersecting tapes,because they never fail to be tightly pressed together before they leavethe bag manufacturing apparatus from above the upper endless belts 17a.

If the material to be contained in a bag has the form of fine powders oris of such type to which the intrusion of moisture or dust isobjectionable, then it is desired that when a network consisting ofsynthetic resin stretched tapes is used in manufacturing a heavy dutybag, one or both sides of said network be caoted with a film asdescribed above. To this end, it is possible to extrude a film from, forexample, a T die and laminate it with a network prepared from only thestretched tapes wound by the aforementioned process. However, if a filmis bonded with the network at the same time the latter is prepared, thenthe manufacturing efficiency will be further increased.

FIGS. 13 to 15 indicate the processes to meet the above-mentionedobject. Referring to FIG. 13, numeral 57 denotes a film holding means. Abroad flat film 58 is spirally wound about the cylindrical form definedby a plurality of endless belts by means of a prime mover $9 andtransmission means 60 at a certain speed interlocking with thetravelling speed of the endless belts l7, in such a manner that there isnot left any gap between the adjacent edges of the wound film (ifrequired, the film edges are allowed to be superposed on each other).Thereafter stretched tapes are spirally wound on said film in the samemanner as shown in FIGS. to 12 to form a heavy duty bag consisting of acombination of a cylindrical network and film.

According to the processes of FIGS. 14 and 15, one or two broad films 62and 63 are guided to the bottom end of endless belts 17 by means ofrollers 64 and 65 and rolled by a guide means'6l in a manner to wrap thecylindrical form defined by a plurality of endless belts 17. Both endsof a single rolled film (FIG. 14) are bonded together and the adjacentends of two rolled films (FIG. are similarly bonded. Under suchconditions, the single or double film is allowed to travel upward overthe surface of said cylindrical form to provide a cylindrical body offilm. In this case, the film edges may overlap each other, if required.Thereafter tapes are wound about the cylindrical film body thus preparedto obtain a network-film composite body as described above. If thesurface of said composite body is further coated with another film,there is obtained a heavy duty bag in which the network is sandwichedbetween two films.

If a heavy duty bag according to the present invention consists ofstretched tapes of synthetic resin combined with yarns or fibres,hydrophilic tapes, stretched tapes made of low softening thermoplasticsynthetic resin, or, foamed stretched tapes prepared from thermoplasticsynthetic resin etc., (or the first mentioned synthetic resin stretchedtapes may be replaced partly or wholly by the above-listed othermaterials depending on their kinds), then there will be obtaineda heavyduty bag having various excellent properties. It will be apparent thatas in the aforementioned case, there may be a bonded a synthetic resinfilm to said network formed of tapes to provide a heavy duty bagconsisting of a network-film composite body.

There will now be described a combined use of the main synthetic resinstretched tapes and other materials as listed above. FIG. 16 is aperspective view of a heavy duty bag consisting of said stretched tapes,to one or both sides of which are bonded strong yarns. FIG. 17 is anenlarged cross section of the bag of FIG. 16. The bag of FIG. 16 isprepared by bonding yarns 66 to one side of a synthetic resin stretchedtape 67, spirally winding said tape 67 in a manner to allow its edges toslightly overlap each other to form an inner cylindrical body, spirallywinding in the opposite direction another piece of synthetic resinstretched tape 67 to one side of which there are bonded said yarns 66 soas to form an outer cylindrical body, bonding together those planes ofthe tapes to which there are not attached said yarns 66 to form acylindrical network and sealing one end of said network to provide abottom 68. The yarns are used in reinforcement and their materials maybe suitably selected from among natural yarns such as those formed ofcotton and hemp, and synthetic fibres such as those of polyamide,polyvinyl alcohol and polypropylene systems. Yarns for reinforcement maybe bonded to stretched tapes in advance, or when said tapes are madeinto a cylindrical body.

FIGS. 18 to 20 are enlarged fractional cross sections of the materialsused in preparing other types of yarnrcinforced heavy duty bag.Throughout these figures, numeral 66 denotes yarns and numeral 67stretched tapes. FIG. 18 presents an arrangement in which there are usedyarns to the outer surface of an assembly of superposed cylindricalbodies prepared from stretched tapes and in the interspace between saidsuperposed cylindrical bodies, FIG. 19 indicates an arrangement in whichthere are interposed yarns between said superposed cylindrical bodiesand FIG. 20 shows an arrangement in which there are disposed yarns onthe outer and inner surfaces of said assembly of superposed cylindricalbodies of stretched FIG. 7 and in the interspace therebetween. Where aheavy duty bag is demended to have a surface resistant to slipping,pi'riiii larly preferable is the one prepared from said assembly, to theoutergouter and inner surfaces of which on are attached yarns.

FIGS. 21 and 22 are elevations, with part broken away, of heavy dutybags prepared from synthetic resin stretched tapes used as a base andhydrophilic tapes incorporated in their interspaces. The bag of FIG. 21comprises a base tape consisting of a synthetic resin stretched tape 69and a hydrophilic tape 70 prepared from paper, cellophane, polyvinylalcohol, etc. These two different types of tape 69 and 70 are spirallywound in alternate arrangement to form an inner cylindrical body 71, andon said body there are again similarly spirally wound said tapes 69 and70 to form an outer cylindrical body 72. Both bodies are bonded togetherand one end of the bonded assembly is sealed to form a bottom 73. Itwill be apparent that the two tapes consituting the cylindrical body 72are spirally wound in the opposite direction to those of the cylindricalbody 71. Since it consists of a hydrophilic tape jointly used with asynthetic resin stretched tape, the aforesaid heavy duty bag has anexcellent moisture-absorbing and dehumidil'ying property, a favourablefeature as a bag for handling agricultural products such as rice andwheat, and moreover retains a desirable mechanical strength due to themeof said stretched tape as a base material.

The heavy duty bag of FIG. 22 is formed of the same kinds of tape asthose of FIG. 21, the only difference being that there is used onehydrophilic tape 76) for three ta e sta eless??? 9:..-

With respect to the heavy duty bags of FIGS. 21 and 22, polyolefinicresins such as high density polyethylene and polypropylene are mostpreferred as the material of a stretched tape 69. At the present moment,however, there is not available any good hydrophilic adhesive for suchpolyolefinic resins. If, therefore, the hydrophilic tape 70 to bejointly used with said stretched tape is coated with an adhesiveoriginally intended for use with polyolefinic resins, then thehydrophilic tape 70 will be reduced in its moisture-absorbing property.Accordingly, where the hydrophilic tape 76) is used in small proportionsrelative to the stretched tape 69 there is no need to coat thehydrophilic tape 70 with any adhesive. Again where large proportions ofthe hydrophilic tape 70 are used with the stretched tape 69, thehydrophilic tape 70 is preferably coated with a thermally operableadhesive in the form of lines or dots, and a heavy duty bag is preparedby thermally melting said adhesive after a cylindrical body is formed ofsaid two types of tapes. Then the resultant bag will be saved from adecrease in its moisture-absorbing and dehumidifying property. Further,there may be interposed a low density polyethylene film between theouter and inner cylindrical bodies according to the application in whichit is desired to use a heavy duty bag If, a synthetic resin stretchedtape is jointly used with another tape prepared from low densitypolyethylene, then the resultant bag will increase in pliability.Moreover, since the low density polyethylene tape has a low softeningpoint, its surface easily melts at the time of thermal bonding, therebyincreasing the bonded strength. Also when the stretched tape is jointlyused with foamed tape such as foamed high density polyethylene orpolypropylene, there will be obtained a soft bag. In addition, such bagwill display a special latticed appearance due to the opaqueness of saidfoamed tape. Further, if there is incorporated a foamed tape containingcontinuous cells obtained by proper adjustment of a foaming operation,then there will be produced a bag having good breatheability. If thejointly used two tapes are made of the same material bearing differentcolours, the resultant bag will display a unique interesting appearance.As mentioned above, suitable selection of jointly used tapes will enablea heavy duty bag to be manufactured in a large variety of form withdifferent properties or interesting visual appeals.

FIGS. 23 and 24 present a heavy duty bag in which at least one of theouter and inner cylindrical bodies is only prepared from a stretchedtape consisting of foamed synthetic resin. This bag is manufactured byspirally winding a stretched tape 74 consisting of foamed thermoplasticsynthetic resin such as foamed polyethylene or foamed polypropylene toprovide inner and outer cylindrical bodies 75 and 76, bonding bothbodies and sealing one end of the bonded assembly to form a bottom 77.In this case, the foamed tape constituting either the inner 75 or outer76 body is spirally wound in the opposite direction to the tape formingthe other body.

In the case where there is used such a foamed tape, excess foaming woulddecrease the mechanical strength of the tape to deteriorate theproperties demanded of a heavy duty bag. Therefore, it is advisable toprepare one of the inner and outer cylindrical bodies from said foamedtape and the other from a nonfoamed tape, so as to maintain the strengthof a heavy duty bag as a whole.

A bag comprising such foamed tape offers a soft touch, and presents animproved visual appeal, because it is reduced in transparency anddelustered. Moreover, said bag is more resistant to slipping due to itsirregular surface.

FIGS. 25 and 26 illustrate a heavy duty bag prepared from a double layerstretched tape, one side of which is composed of a high crystallinitythermoplastic synthetic resin and the other side of which consists ofanother type of thermoplastic resin having a lower softening point thanthe former resin. In this case, the high crystallinity thermoplasticresin includes high density polyethylene, polypropylene and polyamideresins, and the low softening thermoplastic resin consists of lowdensity polyethylene, ethylene-vinyl acetate copolymer orethylene-propylene copolymer. To prevent the molecular orientation ofthe high crystallinity resin layer from being disturbed when the innerand outer cylindrical bodies are bonded together, it is required thatthe softening point of said low softening resin be 20 or over lower thanthat of the jointly used high crystallinity resin. If the double layertapes are so arranged as to allow the mutually facing layers of lowsoftening resin to be bonded together, the material of said resin may befreely chosen. Such double-layer stretched tape may be prepared bysuitably selecting any of the various means, for example, ofsimultaneously processing high crystallinity resin and low softeningresin jointly into a double layer film followed by stretching, coatinglow softening resin on a single layer of high crystallinity resin toform a double-layer film, followed by stretching, or first stretching asingle layer film of high crystallinity resin and then coating lowsoftening resin thereon. Namely, the heavy duty bag of FIGS. 25 and 26is formed by spirally winding a double-layer stretched tape. One side ofwhich consists of high crystallinity thermoplastic synthetic resin 78and the other side of which is made of another thermoplastic resin 79having a lower softening point than the former resin, so as to forminner and outer cylindrical bodies 80 and 81, thermally bonding togethersaid bodies, and sealing one end of this bonded assembly to provide abottom 82. The double-layer tapes constituting the inner and outercylindrical bodies 80 and 81 are spirally wound in opposite directionsin such a manner as to allow the low softening resin layers 79 to faceeach other by being disposed on the outside of the inner cylindricalbody 'and the inner side of the outer cylindrical body.

With a heavy duty bag made of double-layer tapes, the inner and outercylindrical bodies can be firmly bonded with heat without using anadhesive, thus simplifying the manufacturing process. Further, said baghas a fully great mechanical strength due to the incorporation of highmelting high crystallinity thermoplastic resin, while it is made pliantby the use of low softening thermoplastic resin such as low densitypolyethylene.

The group of FIGS. 27 to 29 and that of FIGS. 30A and 308 to 32represent modifications of a bag prepared from a combination of acylindrical network and film. Referring to FIGS. 27 to 29, the bag isprepared by spirally bonding a synthetic resin stretched tape 83 to acylindrical body 84 of synthetic resin film at an angle of 45 withrespect to the axis of said cylindrical body, turning over the lowerhalf of the bonded mass starting approximately with the middle point 85thereof and superposing said half on the upper half and sealing one endof the superposed assembly to provide a bottom 86. Further, it ispossible to allow the stretched tape 83 to be exposed to the outside ofthe bag in an opposite manner to the illustrated case when the aforesaidturnover is made. Such bag is well adapted for use in an application inwhich it is demanded to display resistnace to slipping.

Referring to FIGS. 30A and 308 to 32, a heavy duty bag is prepared byspirally winding synthetic resin tapes 87 about two cylindrical forms 88and 89 of synthetic resin film having slightly different diameters inopposite directions as illustrated in FIGS. 30A and 30B and at an angleof substantially 45 with respect to the axis of the cylindrical form,bonding the tape to the film, superposing two cylindrical forms 88 and89 as shown in FIG. 31 and sealing one end of the superposed assembly toprovide a bottom 90.

In either of the cases represented by the group of FIGS. 27 to 29 andthat of FIGS. 30A and 30B to 32, the handling of a bag is made easier ifits upper edge portion is made into a single integrated layer by joiningthe inner and outer cylindrical bodies, for example, by bonding.

What we claim is:

l. A method for manufacturing a heavy duty bag comprising the steps of:

arranging a plurality of endless belts such that their outer stripsdefine an approximately cylindrical form as viewed horizontally;

causing said belts to travel at the same speed along the axis of saidcylindrical form;

rotating a plurality of tape holding means in opposite directions inturn about the axis of said cylindrical form;

feeding from the holding means theremoplastic synthetic resin tapescoated with a heat-sealable adhesive to spirally wind the tapes aboutthe peripheral surface of the cylindrical form defined by the travellingendless belts in opposite direction turn in a manner to intersect eachother;

bonding the superposed portions of the intersecting tapes to form acylindrical network; and

sealing one end of said cylindrical network;

said bonding step including provisionally and partiallycompression-bonding superposed portions of the intersecting tapes formedon the travelling endless belts by a supplementary roll means to such anextent as to cause the tapes not to separate from one another, and thenfeeding the resultant cylindrical network from the belts between a pairof heated press rolls so as to flatten the network as well as tocompletely bond the superposed portions of the tapes.

2. The method according to claim 1 comprising spreading a thermoplasticsynthetic resin film in advance over the peripheral surface of thecylindrical form defined by said plurality of travelling endless belts.

3. The method according to claim 1 wherein said provisionally andpartially compression-bonding step includes pressing superposed portionsof said intersecting tapes simultaneously on both the inner and outersurfaces of the intersecting tapes by means of said supplementary rollmeans.

1. A method for manufacturing a heavy duty bag comprising the steps of:arranging a plurality of endless belts such that their outer stripsdefine an approximately cylindrical form as viewed horizontally; causingsaid belts to travel at the same speed along the axis of saidcylindrical form; rotating a plurality of tape holding means in oppositedirections in turn about the axis of said cylindrical form; feeding fromthe holding means theremoplastic synthetic resin tapes coated with aheat-sealable adhesive to spirally wind the tapes about the peripheralsurface of the cylindrical form defined by the travelling endless beltsin opposite direction turn in a manner to intersect each other; bondingthe superposed portions of the intersecting tapes to form a cylindricalnetwork; and sealing one end of said cylindrical network; said bondingstep including provisionally and partially compression-bondingsuperposed portions of the intersecting tapes formed on the travellingendless belts by a supplementary roll means to such an extent as tocause the tapes not to separate from one another, and then feeding theresultant cylindrical network from the belts between a pair of heatedpress rolls so as to flatten the network as well as to completely bondthe superposed portions of the tapes.
 2. The method according to claim 1comprising spreading a thermoplastic synthetic resin film in advanceover the peripheral surface of the cylindrical form defined by saidplurality of travelling endless belts.
 3. The method according to claim1 wherein said provisionally and partially compression-bonding stepincludes pressing superposed portions of said intersecting tapessimultaneously on both the inner and outer surfaces of the intersectingtapes by means of said supplementary roll means.